This invention relates to a method of resolving engine cycle ambiguity in a crankshaft position signal of a four-stroke internal combustion engine.
The control of fuel and spark events (among others) in an internal combustion engine requires knowledge of the engine cycle position. A common approach with four-stroke engines is to develop a high resolution position signal based on rotation of the engine crankshaft (which rotates twice per engine cycle), and a low resolution position signal based on rotation of the engine camshaft (which rotates once per engine cycle). In this case, the high resolution crankshaft signal is used to time the fuel and spark, and the low-resolution camshaft signal is used to synchronize the crankshaft signal with the engine stroke cycle.
While the above-described approach works well, various techniques have been developed to either eliminate the camshaft sensor or to provide a level of redundancy in case of a camshaft sensor failure. For example, in the U.S. Pat. No. 5,577,475 to De Backer et al., issued on Nov. 26, 1996, the engine controller assumes an initial crankshaft signal synchronization, supplies fuel to all but a specified one of the engine cylinders to induce misfiring the specified cylinder, and then monitors the engine speed based on the assumed synchronization to identify an acceleration spike attributable to misfiring. If the timing of the acceleration spike indicates that the specified cylinder is misfiring, the assumed synchronization is verified as correct; if the timing of the acceleration spike indicates that a cylinder opposite the specified cylinder is misfiring, incorrect synchronization is indicated, and the assumed synchronization is reversed. This approach can be used effectively, but the acceleration spike calculations are both time consuming and subject to noise-related error, particularly when the engine speed is changing during the induced misfiring. Accordingly, what is needed is a simpler and more reliable method of identifying an induced misfire.
The present invention is directed to an improved method of synchronizing a crankshaft signal with the stroke cycle of a four-stroke internal combustion engine by inducing full or partial misfiring in a specified engine cylinder, and using an assumed synchronization to identify the misfiring cylinder. According to the invention, the crankshaft signal is used to identify reference angular positions of the crankshaft intermediate top dead center positions of consecutive cylinders of the engine firing order, and a time difference between successive reference positions is determined. When the assumed synchronization is such that the current rotation of the crankshaft includes the cylinder in which misfiring is induced, the determined time difference is accumulated in a first accumulator; otherwise, the determined time difference is accumulated in a second accumulator. The presence of misfiring causes the two accumulators to diverge in value, and the direction of such divergence is used to determine if the assumed synchronization is correct or incorrect.